The Marina Freeway segment is a short freeway in southwestern Los Angeles and the nearby suburbs, linking Marina del Rey to the rest of Greater Los Angeles. The limited-access portion runs from Slauson Avenue in southern Culver City to just past Culver Boulevard, where it forms the approximate border between the Del Rey and Westchester neighborhoods of the city of Los Angeles. The route continues westward into unincorporated Marina del Rey as an expressway, terminating at Lincoln Boulevard.

The eastern portion of SR 90 is Imperial Highway connecting La Habra, Brea, Yorba Linda, and Anaheim Hills. A stretch in Yorba Linda between Yorba Linda Boulevard and Orangethorpe Avenue was relinquished to the city in 2002 and built to freeway standards. The city renamed it the Richard M. Nixon Freeway in honor of the 37th President of the United States, Richard Nixon, who was born in Yorba Linda less than half a mile away from the road.

The east segment begins at the intersection of Imperial Highway and Beach Boulevard (State Route 39) in La Habra. It heads east and southeast on Imperial Highway, ending at State Route 91 about 1⁄4 mile (400 m) after crossing the Santa Ana River from Yorba Linda into Anaheim. A portion of the road in Yorba Linda is built to freeway standards; it is now known as the Richard M. Nixon Parkway after the city accepted maintenance in 2002.[1] However, the same state law that authorized relinquishment required the city to "maintain signs directing motorists to the continuation of Route 90".

In the 1964 renumbering, LR 221 was assigned State Route 90, but LR 176 all became part of State Route 42, along with the connecting LR 174 to the west. The piece of LR 176 between I-605 and SR 39 was reassigned to SR 90 in 1965, and the rest east to SR 91 became part of SR 90 in 1968 (at the same time as SR 42 became Interstate 105).

Originally planned as the Slauson Freeway, Route 90 was slated to extend across southern Los Angeles County and northern Orange County, ending at the Riverside Freeway in eastern Anaheim. However, by the 1960s, community opposition had reduced it to what is effectively a minor spur of I-405 to Marina Del Rey (derisively dubbed the "Slauson Cutoff" by comedian Johnny Carson). It was renamed the Richard M. Nixon Freeway for a brief period in the early 1970s, but after Nixon's resignation in the wake of the Watergate scandal, its name was changed to the current appellation.

From I-405 west to Centinela Avenue, the Marina Freeway is 8 lanes wide, before it quickly narrows to 4 lanes at the Culver Boulevard exit. The freeway ends approximately 1⁄2 mile (800 m) west of Culver Boulevard, and continues as an expressway. There has been talk of extending the Marina Expressway slightly west of Lincoln Boulevard (Route 1) to Admiralty Way (approximately 1⁄4 mile, 400 m) to accommodate ongoing expansion of the Marina Del Rey area. Strong opposition to this makes actualization of this plan uncertain.

By 2005, construction on the western end of the Marina Freeway began, to extend the freeway terminus from Culver Boulevard to approximately 1⁄2 mile (800 m) west of Culver Boulevard by building a full interchange at Culver. The freeway extension was completed in early 2007. The freeway extension also allows Route 90 drivers to avoid a traffic signal at Alla Road (just west of Culver Boulevard.). After the end of the freeway, a pair of frontage roads operating as an expressway continues as Route 90 up to Route 1 (Lincoln Boulevard). Signalized intersections occur at Mindanao Way and Lincoln Boulevard, which is the end of the expressway in Marina del Rey. The reason for the extension is to relieve traffic congestion on surface streets.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage. R reflects a realignment in the route since then, M indicates a second realignment, L refers an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see the list of postmile definitions).[8] Segments that remain unconstructed or have been relinquished to local control may be omitted. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.